1. Field of the Invention
The present invention relates to mobile communication networks, and especially to transmission signal defer controlling e.g. in Long Term Evolution (LTE) networks.
2. Description of the Related Art
The evolution of cellular wireless communication systems has been marked with different generations. 1st generation (1G) included analog systems such as AMPS (Advanced Mobile Phone System) and NMT (Nordic Mobile Telephone) cellular phone networks, introduced in the early 1980s. The second generation (2G) introduced digital cellular telephony such as the GSM (Global System for Mobile Communications) standard, introduced in the early 1990s, which was standardized by the European Telecommunication Standards Institute (ETSI). GSM applies Time Division Multiple Access (TDMA) based radio interface. GSM is still the most widespread standard used in mobile communications.
After the 2G networks, 3rd Generation Partnership Project (3GPP) has standardized globally applicable system specification for 3rd generation mobile communication system. An example of such a system is a Universal Mobile Telecommunications System (UMTS) which applies Wideband Code Division Multiple Access (WCDMA) in its air interface. Original chip rate in WCDMA was specified as 3.84 Mcps and the nominal carrier spacing as 5 MHz. In 3GPP release 5, the concept of High-Speed Downlink Packet Access (HSDPA) has been introduced. It is an enhanced communications protocol in the High-Speed Packet Access family which allows higher data transfer speeds and capacity. With HSPDA, data rates up to 4 Mbps for packet switched data are supported. HSPA+ or “Evolved High-Speed Packet Access” is a subsequent wireless broadband standard, and it was defined in release 7. HSPA+ provides further increase in data rates by using higher order modulation methods (such as 64QAM) and by using multiple antenna techniques such as “multiple-input multiple-output” (MIMO) which means employing several antennas both in the transmitter and the receiver.
In release 8, a concept of Long Term Evolution (3GPP LTE) was introduced. Instead of the earlier WCDMA based radio access technology, Orthogonal Frequency Division Multiplexing (OFDM) is applied in LTE. Also, a dual cell HSDPA (DC-HSDPA) is introduced in release 8 which enables single User Equipment (UE) to receive on two adjacent carriers. Dual cell HSDPA is based on a primary and secondary carriers where the primary carrier provides all downlink physical channels together with channels supporting the uplink data transmission, comprising e.g. a first set of High Speed Physical Downlink Shared Channels (HS-PDSCHs) and High Speed Shared Control Channels (HS-SCCHs). The secondary carrier is responsible for transmitting a second set of HS-PDSCHs and HS-SCCHs. Release 8 allows data rate around 42 Mbps when dual cell functionality is used with 64QAM modulation.
Release 9 combined the dual cell HSDPA with MIMO functionality and also extends the dual cell approach to uplink direction. Furthermore, the used carriers may locate in two separate bands for downlink transmission, providing a dual band HSDPA (DB-HSDPA) operation. Bands can be distant, e.g. dual band configuration no 1 in release 9 is specified to represent downlink bands 925-960 MHz and 2110-2170 MHz. This aspect has great effect on planning the UE's RF parts so that the receiver is able to receive in these two bands simultaneously.
Release 9 has further been developed to a standard named as “LTE Advanced”, represented by release 10 and fulfilling all 4th generation system requirements. The LTE architecture comprises an Evolved UMTS Radio Access Network, abbreviated by E-UTRAN. Release 10 specifies for HSDPA a use of three or four carriers in the downlink direction. This means the UE can receive on four adjacent carriers each having a 5 MHz band. It will provide even higher data rates; with MIMO this approach makes possible data rates up to 168 Mbps.
Generally, multi-antenna techniques cannot continuously increase the transmission rate because there are constraints on the UE size, complexity and also a cost limit for the number of antennas that can be installed to a single UE. In order to fulfill the performance requirements for the release 10, carrier aggregation (CA) has been proposed to aggregate two or more component carriers for supporting high data rate transmission over a wide bandwidth. The bandwidth may be up to 100 MHz for a single UE unit.
There are two types of carrier aggregation, continuous and non-continuous. In continuous carrier aggregation, available multiple component carriers are adjacent to each other. For instance, five adjacent component carriers having a 20 MHz frequency band each, may be aggregated into a 100 MHz wide aggregated frequency band for LTE Advanced use. Instead of that, non-continuous carrier aggregation is achieved when such component carriers are separated along the frequency band. For instance, two carriers each of 20 MHz may be aggregated so that one carrier lies on a first band and another carrier lies on different band. This results in wider available total bandwidth without the spectrum being contiguous. Regarding UE's complexity and especially the hardware implementation, continuous CA is easier to implement. However, regarding spectrum allocation policies and licensing of different frequency bands to different usage, non-continuous CA gives more practical approach. However, besides multiple RF receiving units for a UE, also different propagation characteristics need to be taken into account for the non-continuous CA schemes. Transmission blocks from different component carriers can be aggregated at either the medium access control (MAC) layer or at the physical layer. In a MAC layer data aggregation, each component carrier has its own transmission configuration parameters in the physical layer and also an independent Hybrid Automatic Repeat Request (HARQ) entity in the MAC layer. However, in a physical layer data aggregation, one HARQ entity is used for all aggregated component carriers and also transmission configuration parameters should be specified for the entire aggregated bandwidth.
Regarding HARQ in more detail, it is a combination of Forward Error Correction (FEC) coding and error detection. Redundant bits are added to the data stream and with an appropriate error correction method, some errors due to radio channel quality can be corrected. However, in case of bad channel quality, typically not all errors can be corrected by this way, and therefore the corrupted packet needs to be retransmitted. Earlier corrupted packet can also be saved in the receiver, and it can be used together with the retransmitted packet in order to create an error-free packet. HARQ message is therefore a message from the base station to the UE regarding a certain carrier, and a corresponding acknowledgement message ACK (or NACK, “non-acknowledgement”) is created by the UE when receiving the retransmission successfully (or non-successfully). The HARQ messaging can be used in multicarrier transmission so that when the ACK message is sent by the UE as a response to the HARQ retransmission, the test system can determine which downlink carrier the HARQ message relates to.
Regarding radio frequency bands in general, different frequency bands can be licensed to a certain use, or they can be unlicensed. Unlicensed band is basically a shared spectrum where one needs to accept interference from other unknown systems and sources such as in ISM (industrial, scientific and medical) bands. As licensed band operation has been increasingly utilized, portions of the radio spectrum that remain available have become limited. Thus, operators, service providers, communication device manufacturers, and communication system manufacturers, are all seeking efficient solutions to utilize unlicensed shared bands. Communication on an unlicensed shared band is generally based on sharing an available radio channel between different communication devices. Different communication devices may utilize a common radio access technology (RAT), but it is also possible that different communication devices utilize different RATs. In an unlicensed shared band, channel access can be distributed in a manner, where communication devices can be configured to detect a channel, and utilize a channel reservation scheme known to other communication devices in order to reserve a right to access the channel. In such a distributed channel access, a transmitting communication device (e.g. a UE) and a receiving communication device (e.g. “an evolved Node B” or abbreviated later as “eNB”; a base station in 3G and afterwards) are generally not synchronized to any global reference.
Unlicensed bands are naturally shared spectra where one needs to accept interference originating from other unknown systems and interference sources such like different devices applying ISM bands. If deploying unlicensed spectra e.g. for the LTE Advanced networks through some carrier aggregation method, the system needs extensions to be able to operate in such an environment.
One problem in case of uplink carrier aggregation where one or more carriers are allocated on an unlicensed spectrum, the UE may notice after having received a resource allocation request from the eNB (before usage of those resources i.e. during a 4 ms delay from a resource allocate request on the Physical Downlink Control Channel [PDCCH] to actual usage on Physical Uplink Shared Channel [PUSCH]) that there exists significant interference on those unlicensed spectrum resources. In unlicensed band it may be envisioned that also in the future some kind of “listen-before-talk” procedure is desired, thus requiring the device to defer its transmission on unlicensed spectrum. On the other hand, this causes problems in eNB as it waits for the transmission by the UE with certain specified parameters.
Additionally, the eNB itself may also detect notable interference, or noise level increase on resources on the unlicensed spectrum just before the UE or other transmitting is about to start data transmission according to the order by the eNB.
Therefore, there is a need for an efficient signaling method for enabling controlled deferring for the transmission applying carrier aggregation with both licensed and unlicensed frequency bands.